Abstract Synaptic alterations after hypoglycemic seizures The independent roles of hypoglycemia and seizure activity in producing neurological deficits and cognitive impairment in children with insulin-dependent (Type I) diabetes are not completely understood. The studies proposed will test the hypothesis that the combined insult of brain glucopenia with the added metabolic demand of seizures produces increased neuronal death, but also structural synaptic alterations that underlie neuronal dysfunction in the absence of cell death. The objective of this project is to develop in vivo imaging methods to detect and observe serial changes in dendritic spines of cortical neurons following hypoglycemia combined with seizures, to evaluate whether there are synergistic injurious effects. To examine these issues, creation of a cranial window with a novel laser surgery technique combined with two-photon microscopy will enable in vivo imaging of dendritic structures in YFP expressing cortical neurons serially monitored at baseline and during hypoglycemia without and with focal seizures produced by 4-aminopyridine (4-AP). RELEVANCE TO PUBLIC HEALTH: Serial neuronal imaging of synaptic structures in vivo, using an animal model of hypoglycemia combined with seizures in rodents will enable studies relevant to understanding the causes and mechanisms of synaptic structural alterations and dysfunction due to hypoglycemia, seizures, and diabetes in diabetic humans. The imaging method proposed will greatly enhance a variety of studies that employ serial imaging using the cranial window technique with multiphoton microscopy. Understanding mechanisms of diabetes/diabetes complication-induced brain dysfunction may lead to new targets for treatment interventions to prevent or retard cognitive impairment in diabetes. RELEVANCE TO PUBLIC HEALTH: Serial neuronal imaging of synaptic structures in vivo, using an animal model of hypoglycemia combined with seizures in rodents will enable studies relevant to understanding the causes and mechanisms of synaptic structural alterations and dysfunction due to hypoglycemia, seizures, and diabetes in diabetic humans. The imaging method proposed will greatly enhance a variety of studies that employ serial imaging using the cranial window technique with multiphoton microscopy. Understanding mechanisms of diabetes/diabetes complication-induced brain dysfunction may lead to new targets for treatment interventions to prevent or retard cognitive impairment in diabetes.